It is presumed that Bupropion SR works:

• By its capacity to block neural re-uptake of dopamine and/or norepinephrine
  (Fiore et al., 2000).
  
  
• By elevating the levels of these neurotransmitters in the brain.
  
  
• Compensating for the decreased levels of these neurotransmitters that occur during the withdrawal process when nicotine is no longer stimulating norepinephrine and dopamine release (Ascher et al., 1995; Leischow & Cook, 1998).

Bupropion SR helps tobacco users quit in three ways:

• Treats the anxiety and depression that occurs in some tobacco users trying to quit (Covey, Glassman, & Stetner, 1990; Hall, Muñoz, & Reus, 1994; Jarvik & Henningfield, 1988; Jarvik & Henningfield, 1993; Shiffman, 1982; Leischow & Cook, 1998).
  
  
• May act as a replacement of the antidepressant effect that nicotine has on tobacco users (Glass, 1990; Hughes, 1988; Leischow & Cook, 1998).
  
  
• Reduces the severity of some nicotine withdrawal symptoms (Shiffman et al., 2000; Jorenby et al., 1999).